We propose to conduct a phase I study of high-dise radioimmunotherapy using the anti-breast cancer monoclonal antibody humanized-bre-3labeled with 90-yttrium followed by aahpcs in patients with metastatic breast cancer that are refractory to conventional or high dose chemotherapy. Bre-3 labeled with III-indium will be used to imaging these patients. The clinical endpoints of the study will be to define the maximum tolerated dose and dose limiting toxicities of the radioimmunoconjugate. In addition we will study the dosimetry and pharmacokinetics of the radiolable and we will also obtain preliminary estimates of its efficacy in preparation for a phase II study in the future.